The invention relates to musical instrument audio power amplifiers for driving loud speakers. In particular, the invention relates to audio amplifiers for guitars and other musical instruments having discrete digital frequency selective damping factor controls for improving the sound emitted by loud speakers over a full range of audio inputs and particularly at low frequencies near system resonance.
The present invention provides independently variable discrete digital controlled frequency selective damping factor controls especially for guitar amplifiers which incorporate the frequency dependent speaker load into the control loop. The invention is applicable to all types of audio power amplifiers but is particularly useful in solid state audio power amplifiers which sometimes suffer from the inability to produce the necessary strong high and low outputs useful for effectively driving loud speakers in guitar applications.
In accordance with the invention, the output impedance of the amplifier is discretely reduced or adjusted in order to decrease the damping factor.
In a particular embodiment, the invention comprises a solid state audio power amplifier having an input, an output and independently discretely variable frequency selecting damping factor controls. The amplifier drives a load in a foam of a sound producing loud speaker which has a variable impedance characteristic in the audio frequency range. A voltage limit feedback circuit is coupled between the input and output of the amplifier for establishing a minimum level of voltage feedback as at all times. A load current feedback circuit is coupled between the load and the input for establishing a feedback characteristic representative of the load. A presence feedback circuit coupled in parallel with the voltage feedback circuit discretely reduces feedback with increasing frequency above a selected level whereby the damping factor of the amplifier is reduced. A resonance feedback circuit coupled in series with the voltage feedback circuit discretely reduces voltage feedback with decreasing frequencies below a selected level whereby the damping factor is accordingly reduced. The presence and resonance feedback circuits operate independently without interference, so that speaker performance is enhanced at the low and high ends without compromising one or the other. In particular, the amplifier is responsive to reduce the damping factor and to thereby variably and selectively increase the power to the load for enhancing the sound produced by the loud speaker at both high and low frequencies.